Analysis Of Low-middle Temperature Geothermal Power Generation System And Experimental Study On The Performance Of Single Screw Expander

Facing with the more prominent of environmental and energy issues, so theresearch and development of renewable energy sources is necessary. Among renewableenergy, compared with other energy geothermal energy, the geothermal energy has Lowinvestment and operating costs, high utilization factor, almost independent of weatherand climate, stable power generation and so on, so it has a high application development.But the geothermal resources in China, it has little high-temperature geothermalresources, it is mainly the low-medium temperature geothermal and it was widelydistributed. In order to increase the use of the low-medium temperature, it can be usedwith low-medium temperature organic rankine cycle (ORC) geothermal power systemwhich is small and medium-sized. Because single-screw expander has the advantagesof small size and good output performance, it is very suitable for small and medium-sized geothermal power system with ORC. So this paper do some research work aboutlow-medium temperature ORC geothermal power system and experimental study onthe performance of single screw expander.The main content of this paper：(1)Based on the laboratory’s newly developed10kW single-screw expander,combined with the experimental test data and design parameters of the expander, thelow-medium temperature ORC geothermal power generation system was simulatedwith Aspen HYSYS software. With the geothermal water sources from90to150℃,R123, R245fa, R141b,R142b, R113was used as the working fluid in geothermal powersystem. The system thermal efficiency, exergy efficiency, irreversibility and so on wasanalysed. And the calculation showed that, R142b was preferably as working fluid Inthe performance of the system at a certain temperature, but it requires a higherevaporation pressure and is combustible, so the safety and mechanical seals was neededhigher requirements. Considered with system pressure，safty and thermal efficiency,the R123was more suitable as the working fluid in low-medium temperaturegeothermal power generation.(2)Deedly discussion and research was carried on, based on compressed air testbench. The experimental test system was reformed and optimized, air heaters and other equipment was added with the original process. The single-screw expander heatedcompressed air experimental test system was designed and putted up. The performanceof the expander was tested with the heated air of60,80,100,120℃, the expansion ratio,the temperature drop, power, gas consumption rate, irreversibility and efficiency of theexpander were studied. Studies show that, under the same rotational speed, the expanderat the higher air temperature had a better performance，which the output power ishigher, the gas consumption rate is lower, the pressure is relatively larger, thetemperature drop is larger, the efficiency is higher, the irreversibility is smaller.(3)Improvement was made in the latter part of the experiment, on the basis of theheated compressed air test platform, the lubricant oil circulation of the expansionmachine was added. And the performance of the expander with oil circulation wastested. Compared the results of oil circulation and no oil circulation with the airtemperature80℃, we found that the oil circulation expander has better performance,which the output power of the system is larger, the gas consumption rate is lower, thepressure is relatively larger, the temperature drop is larger, the efficiency is higher, theirreversibility is smaller. Analyze the causes of that case， which the expander had abetter performance with oil circulation, partly because the sealing and lubrication roleof oil in the interior of the expander; on the other hand, the pump of the lubricating oilroad improved the performance of the expander.(4)By comparing the data of120℃with no oil circulation and the data of80℃with oil circulation，the expander test with the oil circulation had about the sameperformance with the case at a higher temperature(120℃).Therefore，it is an importantsignificance to study oil circulation of the expander，it can improve performance of theexpander.